##sat ##ura ##ted ke ##tone can undergo a similar cat ##ion ##ic con ##rot ##atory cy ##cl ##ization that is typically referred to as an iso @ - @ na ##zar ##ov cy ##cl ##ization reaction . other such extensions have been given similar names , including homo @ - @ na ##zar ##ov cy ##cl ##izations and vinyl ##ogo ##us na ##zar ##ov cy ##cl ##izations . because they overs ##ta ##bil ##ize the pen ##tad ##ien ##yl cat ##ion , β @ - @ electron dona ##ting sub ##sti ##uen ##ts often severely imp ##ede na ##zar ##ov cy ##cl ##ization . building from this , several electro ##cy ##cl ##ic ring openings of β @ - @ al ##ko ##xy cy ##cl ##open ##tan ##es
##saturated ketone can undergo a similar cationic conrotatory cyclization that is typically referred to as an iso @ - @ nazarov cyclization reaction. other such extensions have been given similar names, including homo @ - @ nazarov cyclizations and vinylogous nazarov cyclizations. because they overstabilize the pentadienyl cation, β @ - @ electron donating substiuents often severely impede nazarov cyclization. building from this, several electrocyclic ring openings of β @ - @ alkoxy cyclopentanes